5000 lira, reduced weight (3.5 instead of 6 grams).
Krause says this type exists for 1999, but not 1998. However, I have a 1998.
It is the reduced version, much lighter and thinner (no need to check). But for proof, here's it on the scale:

Date close-up. Definitely not a '99.

Could you check your catalogs and collections for this type?
It's KM#1029.1 (normal) and 1029.2 (reduced).